The propagation of suspension and anchorage dependent cells in hollow fiber bioreactors is variously described in the prior art. In general, known procedures entail the use of bioreactors comprising a plurality of media permeable parallel hollow fibers surrounded by an extracapillary space (ECS). Cell growth medium passed through the hollow fiber lumens permeates the lumen walls to support cell growth in the ECS. See, e.g. U.S. Pat. Nos. 3,821,087; 4,439,322 and Ramsay et al. In Vitro 20:10 (1984).